Background: Newborn infants are susceptible to hypothermia during bathing due to environmental conditions. Purpose: This study examined the effects of 2 common newborn bathing methods used in Turkey, underrunning water bathing (URWB) and immersion tub bathing (ITB), on infant heart rate (HR), oxygen saturation, and body temperature. Methods: In this randomized controlled study, 44 newborns were allocated to the ITB group and 36 newborns to the URWB group. Body temperature, HR, and oxygen saturation values of the newborns were compared between groups every hour during 4 hours before the bath to evaluate infants' vital sign stability. All measurements were compared at 10, 20, 40, and 60 minutes after the bath too. Results: No statistically significant differences were found in vital signs performed prior to bathing as compared with after bathing; however, changes in oxygen saturation at 20 minutes after the bath were significantly higher in the ITB group (P < .05). Conclusion: Although both bathing methods decreased overall infant body temperature, ITB positively affected newborn oxygen saturation and HR to a greater degree compared with URWB. Implications for Practice: ITB facilitated maintenance of oxygen saturation and HR during the bath and should be preferred for newborn infants to feel more relaxed. Implications for Research: These findings indicate a need for additional studies with larger sample sizes to further evaluate the effect of different bathing methods on newborn comfort.